One of the most interesting additions to the card is actually something we already have on the HD 6900 series cards. The Dual-BIOS switch that we saw launch with the HD 6900 again appears on the HD 6990. This time it's a little more exciting, though, as AMD call it "AUSUM" or Antilles Unlocking Switch for Uber Mode.

The card will ship in "Position 2" and that will place the card at the factory core clock which is 830MHz. This is closer to the 800MHz clock of the HD 6950 than the 880MHz clock that the HD 6970 offers. Moving to "Position 1" brings with it not only a push to 880MHz, but an adjustment in the core voltage that moves from 1.12v to 1.175v.

The increase in voltage will bring with it the ability to achieve even more speed, though, with AMD saying we'll be able to achieve clock speeds in excess of 900MHz on the core. During all this, the 4GB of GDDR5 remains unchanged and comes in at a 5000MHz QDR clock on a 256-bit bus. This is the same speed that the HD 6950 comes in at.

What's so important in knowing how fast the card will run at is the amount of Stream Processors the card will carry. Like the HD 5970, AMD has done the right thing and used the highest single GPU card as its base. That means that the 3072 Stream Processors and 192 Texture Units equate to the same amount as two HD 6970s.

This tells us that out of the box you're going to receive performance in between a HD 6970 CF setup and HD 6950 CF setup. It will be slower than the HD 6970 CF setup, even in "Position 1", as the memory clock is 500MHz QDR slower, but faster than the HD 6950 CF setup because the core is clocked higher in both positions and more Stream Processors and Texture Units are on offer.

This is exactly what people wanted with the "Dual BIOS" switch and I think we're going to see some companies really go nuts with it, especially when we start getting some massive triple slot cooling solutions on the card.

It seems that the "Dual BIOS" switch along with PowerTune allows AMD to get around some of the limitations that we normally see on these ultra-high end video cards. Below you're able to see exactly what flicking that switch to "AUSUM" mode does.

We told you what it does as far as clocks go, but above you're also able to see the extra bandwidth that is offered. More importantly is you're able to see what happens to power draw which turns the card from a 350 Watt "Typical Gaming" / 375 Watt "Maximum Power" setup to a 415 Watt "Typical Gaming" / 450 Watt "Maximum Power" one.

In CrossFire that translates to 900 Watt of Video Card Power Draw, or a really expensive and high quality power supply that exceeds well into the 1000 Watt mark with something like an AX1200 from Corsair being a necessity.

That's really a lot of power, but for years we've been hearing people whine about the fact that people buy 1000 Watt power supplies and have no use for them. Well today, that changes, as you're going to need over 1000 Watt to deal with a dual card setup that equates to four GPUs.

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